Continued support is requested to examine the morphology, synaptic relationships, immunocytochemistry, and physiological response properties of neurons in the cerebral cortex of rat, cat and monkey. The goal is to obtain information about the neuronal circuits in the cerebral cortex. A Golgi-EM technique will be used to examine individual neurons. Thus, their forms will be determined with the light microscope, and their cytological characteristics and synaptic relationships with the electron microscope. This study will include a determination of the types and distribution of synapses formed by the axons of the neurons. When the study of neurons in rat visual cortex is completed, the neuronal composition of that cortex can be determined. Through immunocytochemistry the distribution and identity of glutamate decarboxylase, substance P and vasoactive intestinal polypeptide (VIP) positive components in the cortex will be evaluated. Some of the extrinsic connections of cortical neurons will also be investigated, with particular attention being paid to the connections between area 17 and the peristriate areas, and the callosal connections of these latter areas in rat cortex. This data will be correlated with the results obtained from intracellular recordings taken from neurons in area 18 contained in brain slice preparations. The neurons will be activated by electrical stimulation of the callosal and intracortical connections and they will be identified by intracellular injections of markers. Blocking inhibitory synapses and applying neurotransmitters to the preparation will allow us to assess the role that intrinsic neurons might have in modifying the responses of these neurons.